JPH0326591B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method for detecting a decrease in the absolute level of light intensity and a decrease in relative light intensity in the peripheral area with respect to the central area in an image reader using a fluorescent lamp as a light source.

[Technical Background] Image readers are widely used as input means for characters, graphics, bar codes, etc. in data processing devices, or as image input units in facsimile machines, copying machines, and the like.

There are various types of image readers, such as a laser type and a fluorescent lamp type, and the present invention is particularly related to the latter type. In the fluorescent lamp method, a fluorescent lamp is used as a light source to illuminate the document surface, and an image sensor such as a CCD detects the reflected light to extract an image signal.

This fluorescent lamp system has drawbacks such as a decrease in light intensity due to deterioration of the fluorescent lamp, and a difference in light intensity between the central area and the peripheral area.

For this reason, conventionally, CCD
The white level reference of the entire screen is uniformly corrected by monitoring the output white level signal, and methods are used to uniformize the light intensity distribution in advance using a shading plate for peripheral light intensity.

FIGS. 1a, b, c, and d are explanatory diagrams of light amount distribution correction using the above-mentioned shading plate.

Figure 1a shows the optical system of the image reader, 1
2 is a fluorescent lamp, 2 is a document surface, 3 is a lens, 4 is a shading board, and 5 is a CCD. Also, X indicates the main scanning direction, and Y indicates the sub-scanning direction. Figure b shows the output signal level V of the CCD for a white screen when no light intensity distribution correction is performed. Note that the number of pixels in the scanning direction X is 2048 dots. As shown in the figure, for the same white screen, the central area has a larger amount of light and is brighter than the peripheral area. Figure c is a front view of the shading plate 4, which is placed after the lens 3 in order to equalize the imbalance in the light intensity distribution shown in figure b, and is designed to block more light in the center than in the peripheral areas. It has a shape. d shows the CCD output signal level when the light intensity distribution is corrected using the shading plate 4. FIG.

However, when fluorescent lamps deteriorate over time, the ends of the tubes in particular turn black, and the light intensity distribution characteristics corrected using a shading plate deviate from the peripheral areas, resulting in areas with flat characteristics, as shown in Figure 2. It gradually becomes narrower. Since such deterioration is limited to a portion of the screen, it cannot be improved using the conventional method of uniformly correcting the white level standard of the CCD output signal for the entire screen, and the image There is a risk of quality deterioration such as reading errors.

[Object and structure of the invention]

The purpose of the present invention is to prevent a fluorescent lamp type image reader from decreasing when the absolute level of the light amount and the relative level of the heavily variable light amount over time exceeds a permissible range.
By automatically detecting this and issuing a warning, it is possible to urge the fluorescent lamp to be replaced at an early stage before the image reading quality deteriorates, and to provide a concrete means for this purpose.

In an image reader that uses a fluorescent lamp as a light source, the present invention has a reference white display surface provided along the main scanning direction at a position preceding the image reading area, and a reference white display surface provided along the main scanning direction at a position preceding the image reading area. , First, means for scanning the reference white display surface, means for sampling the image sensor output at the center and peripheral areas during scanning of the reference white display surface, and storing the respective light amounts; Means for extracting the light amount at the center and the light amount at the periphery and comparing the absolute level of each light amount with a predetermined tolerance value, and calculating the ratio between each absolute level of the light amount at the center and the light amount at the periphery and converting it into a relative level. The present invention is characterized in that it is equipped with means for comparing with other permissible values determined as above, and outputs an alarm signal when the absolute level or relative level of the amount of light exceeds the permissible value.

[Embodiments of the invention]

The details of the present invention will be explained below with reference to Examples.

FIG. 3 is an explanatory diagram of the basic principle of the present invention.
In Figure 2, 6 is the CCD reading screen, 7 is the image reading area, 8 is the reference white display area,
9, 9', 9'', ... are scanning lines, X is the main scanning direction, Y
indicates the sub-scanning direction. Further, A and B are sampling points of the reference amount of white light.

As shown in the figure, a reference white display area 8 used for checking the amount of light is provided at the beginning of the image reading area 7. Prior to the start of image reading, this reference white display area is scanned by the scanning line 9.

Here, sampling point A is placed at the periphery of the scanning line, and sampling point B is placed at the center. FIG. 4 shows the relationship between the positions of sampling points A and B in FIG. 3 on the light intensity distribution characteristic and the corresponding sample amounts a and b. Also, S _A ,
S _B is a sample and hold control signal and indicates timing position relative to scan line 9.

First, in order to check for a decrease in the absolute level of the amount of light, a sample amount a of the peripheral white level or a sample amount b of the center white level is compared with a predetermined reference voltage that provides an allowable value. Here, it is assumed that the sample amount a of the peripheral white level is compared with the reference voltage P. In this case, a>P is within the permissible range, and an alarm may be issued when aP is reached.

Next, the relative level a/b of the sample amount a of the peripheral white level with respect to the sample amount b of the center white level.
Check for decrease in Q is the relative level tolerance.
Then, a/b>Q is the allowable range, and a/b
It is sufficient to issue an alarm when bQ is reached. In addition,
It is more convenient to handle this conditional expression in the form aQ·b. For example, 0.9 is used as the value of Q. In this case, an alarm is issued when the value of a drops to 90% or less of the value of b.

FIG. 5 is a block diagram of an apparatus according to an embodiment of the present invention. In the figure, 10 is a glass plate, 11 is a document abutting plate, 12 is a reference white display surface, 13 is a document, 14 is a carrier, 15 and 16 are fluorescent lamps, 17 to 19
20 is a reflecting mirror, 20 is a lens, 21 is a shading plate, 22 is a CCD, 23 is a home position sensor, 24 is a timing control circuit, 25 is a line buffer, 26 and 27 are sample/hold circuits, 28 is a potentiometer, 29 and 30 are comparison circuits, and S _A and S _B are sample and hold control signals.

The reference white display surface 12 corresponds to the reference white display area 8 shown in FIG. 3, and is formed by pasting or coating a white plate on the back side of the original abutting plate 11. When the carrier 14 is in the home position, this reference white display surface is the CCD
22.

Next, the operations and functions of each part will be explained.

After the original 13 is placed face down on the glass plate 10, the apparatus is started. The carrier 14 moves from its home position to the right in the figure, that is, in the sub-scanning direction Y. During this time, the fluorescent lamps 15 and 16 illuminate the document surface, and the reflected light is reflected by the reflecting mirrors 17 and 1.
The light is reflected by the light beams 8 and 19, passes through the lens 20 and the shading plate 21, and enters the CCD 22.

The output of the CCD 22 is supplied to a line buffer 25 and sample/hold circuits 26 and 27.
The timing control circuit 24 controls the CCD 22, line buffer 25, and sample/hold circuits 26 and 27 based on the home position signal and clock signal from the home position sensor 23.
etc., to control their operations.

The sample and hold control signals S _A and S _B are set by the timing control circuit 24 as shown in FIG. 4 in correspondence with sampling positions A and B in FIG. 3, respectively, when the carrier 14 is located at the home position. occurs in As a result, in the sample and hold circuits 26 and 27, the CCD
Sample amounts a and b are extracted from the output signal and held. The sample and hold circuit is a conventionally well-known circuit.

The output signal of the sample-and-hold circuit 26 is a, which is compared with the reference voltage P in the comparator circuit 29.
In the case of P, an alarm signal ALM is output.

The output signal of the sample-and-hold circuit 27 is b, which is divided by the potentiometer 28 with a voltage division ratio Q, becomes Q·b, and the comparison circuit 30 outputs the signal a.
compared to Then, when aQ·b, an alarm signal ALM is output. In the comparison circuits 29 and 30,
Well-known circuits using operational amplifiers can be used.

The alarm signal ALM may cause an alarm lamp to light up, or may cause an interrupt to be made to the host.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to check the reduction in light intensity due to blackening of the fluorescent lamp in the image reader each time the image reader operates, and to detect and warn at an early stage, thereby improving the image quality of the read image information. The decline can be prevented.

[Brief explanation of drawings]

Figures 1a to d are explanatory diagrams of a conventional light intensity distribution correction method for a fluorescent image reader, Figure 2 is an illustration of a reduction in light intensity due to deterioration, Figure 3 is an explanatory diagram of the principle of the method of the present invention, and Figure 4 is an illustration of the principle of the method of the present invention. The figure is an explanatory diagram of light quantity sampling in the method of the present invention, and FIG. 5 is a configuration diagram of an apparatus according to an embodiment of the present invention. In the figure, 10 is a glass plate, 12 is a reference white display surface, 13 is an original, 14 is a carrier, 15 and 1
6 is a fluorescent lamp, 22 is a CCD, 23 is a home position sensor, 24 is a timing control circuit, 25 is a line buffer, 26 and 27 are sample and hold circuits, 28 is a potentiometer, and 29 and 30 are comparison circuits.

Claims (1)

[Claims] 1. In an image reader that uses a fluorescent lamp as a light source, there is a reference white display surface provided along the main scanning direction at a position preceding the image reading area, and when the image sensor scans the image reading area, the above reference white is first displayed. a means for scanning a display surface; and in scanning the reference white display surface;
A means for sampling the image sensor output in each of the central and peripheral areas and storing the respective light amounts; and a means for extracting the stored central and peripheral light amounts and setting the absolute level of each light amount to a predetermined tolerance value. and a means for calculating the ratio between each absolute level of the central light amount and the peripheral light amount and comparing this as a relative level with another predetermined tolerance value, the absolute level of the light amount is determined. Alternatively, a method for detecting a decrease in light intensity of an image reader is characterized in that an alarm signal is output when the relative level exceeds a permissible value.